DE 40 25 267 A1 describes a check valve for a gas line, wherein a check plate is biased against a valve seat by a plate spring element. A limiting element adjustable, by means of an actuator, abuts the check plate in the closed state of the valve with interposition of the spring, while, in the open state, this limiting element abuts a fixedly installed maximum stroke limit. This limiting element is displaceable between these two maximum positions. With such valves, the problem arises that the check plate tends to stick to the valve seat either due to excessive soot deposits or due to freezing.
DE 94 15 251 U1 proposes a check valve for a gas line, wherein the stroke limiting element is provided with one or more recesses in which individual helical springs are arranged that bias the check plate against a valve seat. In addition, the limiting element has an axial collar in the outer circumferential portion, which in the closed state of the valve also abuts a valve seat. In order to avoid a sticking of the check plate or the limiting element to the valve seats, these are provided with a PTFE layer intended to prevent baking. Further, this valve comprises a guide element on which the check plate slides and which is fixedly secured to the valve rod. This guide element has a collar at the end facing towards the actuator, wherein the check plate abuts this collar only upon assembly.
Forming the valve seats from PTFE, or with a PTFE coating, represents an additional manufacturing step and, thus, entails additional costs. Moreover, in long-term operation of the valve, coking or frozen water can settle in the area next to the valve and may grow beyond the same with time, which may also lead to a sticking of the check plate to the valve seat.
Therefore, it is the object of the present invention to provide a combined check and control valve, wherein an adhering check plate can be reliably released, while additional costs or additional manufacturing steps are to be avoided as far as possible.